A. Related Applications
There are no applications related hereto filed in this or any foreign country prior to the filing hereof.
B. Field of Invention
This invention relates generally to bits for impact type drills and more particularly to a helical rib structure thereon to aid in preventing collaring during bit withdrawal.
C. Description of Prior Art
In the percussion drilling of rock an ever present problem is that of removing the drill from a hole without collaring or binding in the hole already drilled. In the case of pneumatic type drilling this problem recently has been accentuated by safety regulations requiring that particulate matter be dampened or wetted to aid in preventing its becoming a health hazard. When the dust and particles are wetted they tend to agglomerate in a drilled hole behind the drill bit and when the bit be removed through that hole the probability of collaring is substantially increased, with resultant inefficiency and often substantial losses of both labor and materials. The instant invention seeks to lessen or alleviate this problem.
The normal impact type rock drill has a bit of larger diameter carried at the end of a shaft or drill stem of smaller diameter. The drill bit to be functional must have a rearward (toward the drill stem) taper generally of about three degrees so that the forwardmost drilling portion is of a slightly greater diameter than the rearward body portion of the bit. When a bit of this somewhat truncated conic configuration is extracted from a drilled hole there is a tendency for any particulate debris in the hole to become wedged between the bit and the walls defining the hole, oftentimes to make extraction of the bit difficult or even impossible. This happening in the vernacular of the drilling arts is commonly called "collaring." In the dry drilling of holes with the use of appropriate pneumatic pressure to blow particulate debris back out of the hole, collaring though an ever present problem is not too severe a problem. When the particulate drilling debris is wetted enough to comply with modern day health safety standards, however, it tends to agglomerate on the sides of the drill hole rearwardly of the bit and to remain there prior to the extraction of the bit no matter how much air pressure may be applied through the hole. Since the advent of these safety standards requiring the wetting of drilling debris, substantially more time has been required to remove the bits from drilled holes than was the case before those safety standards, with the same equipment. In fact the amount of footage that a driller can drill in a given period of time has been reduced in some cases by thirty to fifty percent depending upon the parameters of the particular situation.
Especially since the advent of extremely hard carbide type drilling bits it has become feasible to drill holes up to several hundred feet in length with impact drills and because of this compound type drill stems have come into common use. Generally these drill stems are threadedly attached to each other and to the drill bit. This threaded attachment of drill stem to drill stem or drill stem to bit has become quite specialized so as to provide a quick connecting or disconnecting joint and one which concentrates impact forces on shoulders or surfaces perpendicular to the direction of impact so that the impact is not carried directly by the threads. This construction has provided a compound drill with parts quite readily disconnectible that may be rotated in only one direction, all to compound the problem of removing the drill from holes and of collaring during the process. Before the advent of compound drill stems commonly unitary drill stems could be rotated successively in opposite directions to aid removal and prevent collaring during the withdrawal operation, but the compound, threadedly connected type of drill stem has made this impossible. Again, commonly with impact rock bits heretofore known, one or more helical ribs have been provided on the rearward diametrically smaller part of the bit angled in such fashion as to aid in moving particulate matter being drilled rearwardly out of the hole when the bit be rotated in the direction to tighten its threaded connections. When such a bit is being withdrawn from a hole these helical ribs will tend to move debris on the drill hole walls rearwardly out of the drilled hole ahead of the bit as it is extracted therefrom, again to make the removal more difficult and increase the probability of collaring the bit in the hole.
My invention seeks to alleviate these problems by providing a typical modern day impact rock drill bit with helical ribs on the diametrically smaller rearward portion so angled as to have a screw effect causing particulate matter in the hole rearwardly of the drill to be moved past the drill and into the forwardmost drilled portion of the hole when the drill be rotated in a direction to tighten the threaded connections of the drill stem during the removal process. My bit then instead of moving debris in the hole in front of the bit as it is extracted tends to move the material through the flutes in the drill past the drill bit so that the debris remains in the hole to make bit removal easier, allow rotation of the bit upon removal and tend to lessen the probability of collaring the bit during the removal process. My invention lies in the unique combination of particularly configured structures that allow this function and not in any one of these structures per se.
Heretofore the basic concept of using helical ribs to move particulate matter in a drilled hole forwardly into the hole and past a bit during the extraction process was disclosed by Atkinson in U.S. Pat. No. 2,579,720. The Atkinson device, however, differs in function from the instant invention in that it, to be operative if at all, would require a unitary drill stem since that stem would have to be rotated opposite its normal drilling rotation during the extraction process to cause particulate matter in the hole to pass forwardly into the already drilled hole and past the bit being extracted. This counter-rotation is impossible with present day compound drill stems as the drill stem would come apart and a forward part of the drill would be lost in the hole. To date, at least, no satisfactory locking device has been found to lock the threadedly connected drill stem or bit together against counter-rotation. The Atkinson device also differs in structure from the instant invention in that Atkinson's helical ribs are not continuous from the cutting portion of the drill rearwardly, but rather leave a space between the cutting portion of the drill and the forward part of the ribs which tends to allow collaring within that space and even to increase the probability of collaring above that existing if the ribs were not present. The helical ribs of the instant invention are continuous from their rearwardmost portion forwardly to the drilling portion of the bit and are substantially of the same radius as the gauge clearance of the bit to lessen the probability of collaring. The cross-sectional shape of the ribs of the instant invention is rectangular rather than curvilinear as in the Atkinson device so as to tend to move particles parallel to the drill hole rather than allowing their passage over the drill ribs. The instant invention thus differs both in structure and function from the Atkinson device.